This study will compare brain and hormone responses to food images (and food) in women who undergo: (1) gastric bypass surgery; (2) principally restrictive surgery (laparoscopic adjustable gastric banding or laparoscopic sleeve gastrectomy); or (3) no weight loss surgery, with the intent of remaining relatively weight stable (within 10-15 lb of your present weight). The investigators will use magnetic resonance imaging (MRI) to see how the brain responds to pictures of food and to consuming a liquid meal replacement. The investigators wish to determine whether the two surgeries have different effects on appetite, as observable in the brain, and whether the possible effects on appetite differ from those in participants who have a similar body weight but remain relatively weight stable. The investigators also will draw blood to determine how "hunger" and "fullness" hormones change after eating and to see if there are any differences among the three groups. The study is being sponsored by the National Institutes of Health (NIH).